Energy expenditure (a major component of body weight) is regulated through a complex regulatory network formed by signaling and transcriptional components that control bioenergetic/metabolic function. Skeletal muscle and beige/brown adipose are key tissues that account for a large fraction of energy expenditure. Adrenergic/cAMP signaling is one of the powerful pathways that affect energy balance and cellular bioenergetics. Defects in components of the signaling/transcriptional and mitochondrial bioenergetic system is sufficient to promote obesity and associated disorders such as type 2 diabetes and atherosclerosis. Importantly, maintenance and activation of mitochondrial bioenergetic function strictly depend on basal and regulated transcription of nuclear genes encoding for mitochondrial proteins. Among the transcriptional regulators of these mitochondrial processes are the PGC1 family of coactivators and transcription factors including Nuclear Respiratory Factors, Hormone Nuclear Receptors and YY1. In the last years, our laboratory has identified the transcription factor YY1 as a key regulator of nuclear mitochondrial genes that has a major impact in mitochondrial bioenergetic capacity, both in cultured cells and in animals. Depending on YY1 phosphorylation at specific sites, phospho-YY1 forms an active complex on mitochondrial genes through recruitment of PGC1. In contrast, dephospho-YY1 forms a repressor complex through interacting with Polycomb Proteins that suppresses the expression of mitochondrial genes. Importantly, one of the signals that govern YY1-dependent phosphorylation interaction is the cAMP pathway. Based on these findings, the major goal of this proposal is to identify the regulatory mechanisms driving mitochondrial gene expression through YY1 transcriptional complex and to assess the functionality using in-vivo mouse models of obesity and diabetes. We have three Specific Aims: Aim 1 proposes to perform molecular mechanistic analysis of how the YY1 transcriptional complex controls mitochondrial function. Aim 2 is devoted to carry out cellular and functional mitochondrial bioenergetic and metabolic analysis mediated by the YY1 transcriptional protein complex in skeletal and adipose cultured cells. Aim 3 is focused to perform in-vivo metabolic and energetic analysis mediated by the YY1 transcription factor in skeletal muscle and adipose tissues. We will use genetic mouse models with gain and loss-of-function of YY1 in these tissues. The outcomes of these studies will provide the identification of the molecular mechanisms by which the YY1 transcriptional complex regulates mitochondrial bioenergetic capacities and how defects in this complex result in dysregulated mitochondrial function and energy balance. Based on the fact that these pathways are altered in metabolic diseases such as obesity and diabetes, studies proposed in this grant application might translate into potential therapies.